1. Field of the Invention
The present invention relates to an energy beam curable epoxy resin composition which is curable upon exposure to an energy beam such as an ultraviolet ray or an electron beam, a stereolithographic resin composition using said resin composition and a stereolithographic method. More specifically, the present invention relates to an energy beam curable epoxy resin composition to give the cured resin, which has chemical resistance, water-resistance, humidity-resistance, good adhesive property and reduced shrinkage on curing, a stereolithographic resin composition using said resin composition and a stereolithographic method.
2. Related Art
Recently, resin compositions, which are curable upon exposure to an active energy beam such as an ultraviolet ray or an electron beam, are used in various applications such as paint and varnish, coatings, adhesives, sealing compounds and the like. A photo-curable epoxy resin composition is known as one of said energy beam curable resin compositions as described in, for example, Japanese Patent Application No. SHO 63-113022, No. HEI 3-77210, Japanese Patent Application Laid-open No. HEI 1-149848, No. HEI 2-114022, No. HEI 4-266,985.
The photo-curable epoxy resin composition is not influenced with oxygene on curing, being unlike a radically polymerizing photo-curable resin, has superior physical properties such as an adhesive property in the cured articles, and then is expected to be used in wide applications.
This photo-curable epoxy resin composition is composed essentially of an epoxy resin and a photopolymerization initiator. Onium salts are known to be used as a photopolymerization initiator.
Alicyclic epoxy ester compounds, which typically include 3,4-epoxy cyclo-methyl-3,4-epoxy cyclohexane carboxylate "Cylacure UVR-6110, Union Carbide Corp., or Ceroxide-2021, Daicel Chemical Industries LTD." and bis(3,4-epoxy cyclohexylmethyl) adipate "Cylacure UVR-6128, Union Carbide Corp.", are used as a main component for a photopolymerization initiator-curable epoxy resin, since they have preferable reaction rate and physical properties.
A stereolithographic method is a technique, as described in Japanese Patent Application Laid-open No.SHO 60-247515, wherein a given portion of photo-curing resin placed in a vessel is exposed continuously to a beam such as argon, helium-cadmium or semiconductor laser from above to cure the exposed portion, in order to produce a desired plane of cured layer. Then the cured layer is overlaid with another layer of the photo-curing resin, which is then photo-cured in the same manner to produce a second cured layer which continuously overlaps the first layer; and the same process is repeated to finally obtain a desired three-dimensional solid shape.
As resins previously used for the above-described stereolithographic method, mention may be made of radically polymerizing resin compositions and, for example, Japanese Patent Application Laid--open No.HEI 2-228312 and No.HEI 5-279436 disclose a stereolithographic resin composition composed mainly of (meth)acrylic resin. Further, Japanese Patent Application Laid-open No.HEI2-145616, with the aim of reducing deformation, discloses a stereolithographic resin which contains liquid resin and fine particles whose difference in apparent specific gravity is less than 0.2. For producing moldings at higher precision, Japanese Patent Applications Laid-open No.HEI 3-15520 discloses a composition comprising an unsaturated ethylene-derivative monomer, a photo-initiator, and a potentially insoluble, potentially radioactive polarizing substance, and Japanese Patent Applications Laid-open No.HEI 3-41126 discloses a composition comprising an unsaturated ethylene-derivative monomer, a photo-initiator, and a potentially soluble radio-polarizing substance, respectively. In addition, Japanese Patent Application Laid-open No.HEI 4-85314 discloses a resin composition comprising a silicone urethane acrylate, a compound having multifunctional ethylene-type unsaturated bonds, and a polymerization initiator.
Another stereolithographic resins are known cationically polymerizing resin composition. For example, Japanese Patent Application Laid-open No.HEI 1-213304 discloses a cationically polymerizing resin composition characterized by comprising a cationically polymerizing energy beam curable organic compound and a energy beam sensitive cationic polymerization initiator. Japanese Patent Application Laid-open No.HEI 2-28261 discloses a resin comprising a cationically polymerizing energy beam curable organic compound and a portion of a radically polymerizing radio-curing organic compound, which exhibits reduced shrinkage and improved resolution. Also, Japanese Patent Application Laid-open No.HEI 2-80423 discloses a resin composition comprising an epoxy resin, a vinyl ether resin, an energy beam sensitive cationic polymerization initiator, a radically curing resin, and an energy beam sensitive radical polymerization initiator. In addition, Japanese Patent Application Laid-open No.HEI 2-75618 discloses a stereolithographic resin composition characterized by comprising a cationically polymerizing energy beam curable organic compound, an energy beam sensitive cationic polymerization initiator, a radically polymerizing energy beam curable organic compound, an energy beam sensitive radical polymerization initiator, and a polyester having hydroxyl groups.
Among the conventional stereolithographic resin compositions as described above, photo-curable epoxy resin compositions composed mainly of an alicyclic epoxy ester compound generally have improved brightness, heat resistance, chemical resistance and reduced shrinkage on curing in cured articles and thus are used for paint and varnish, coatings, adhesives, sealing compounds and the like. However, the cured articles are required to improve some properties such as alkali-resistance, water-resistance and adhesive property and also express the change in dimensions due to moisture absorption.
Further, any of a radically polymerizing resin and a stereolithographic resin composition composed mainly of it is prevented from curing under oxygene, which results in low degree of cure on curing, so that it is necessary to carried out "post cure process" by ray or heat, which is necessarily concerned in curing of mold. In the post cure process, however, the moldings has such a disadvantage as being apt to deform. Further, these resins show large shrinkage on curing, which makes it difficult to obtain a molding with desirable dimension.
Furthermore, cationically curable stereolithographic resins as described in Japanese Patent Application Laid-open No.HEI 1-213304, No.HEI 2- 28261 and No.HEI 2-75618, have such superior charasteristic properties that the post cure process are not necessary and the deformation are little, as the curing proceeds through an active group even after the beam to be exposed are shut down, and it is also easy to obtain a molding with desirable dimension because of small shrinkage on curing. However, these resins have such disadvantages that they have insufficient sensitivity to an energy beam to be exposed, and the cured articles show the deformation by humidity-absorption because of its humidity-absorption.
On the other hand, Japanese Patent Application Laid-open No.SHO 58-172387 discloses a method of producing 2,2-dicyclohexenylpropane di-epoxide, and Japanese Patent Application Laid-open No.SHO 48-29899 discloses an epoxy resin composition consisting of methylene bis(3,4-epoxy cyclohexane) and polycarbonic acid anhydride, which can be cured by heating. However, it has never been known hitherto, whether these alicyclic epoxy compounds are suitable for photo-curing or lithographic molding, or not.
Therefore, the object of the present invention is to provide an energy beam curable epoxy resin composition, a stereolithographic resin composition and a stereolithographic method, which can give the improved cured article, having superior physical properties and a high dimensional stability under humidity absorption.